pgsql: Fix calculation of how much shared memory is required to store a

Fix calculation of how much shared memory is required to store a TOC.

Commit ac883ac453 refactored shm_toc_estimate() but changed its calculation
of shared memory size for TOC incorrectly. Previously this could cause too
large memory to be allocated.

Back-patch to v11 where the bug was introduced.

Author: Takayuki Tsunakawa
Discussion: https://postgr.es/m/TYAPR01MB2990BFB73170E2C4921E2C4DFEA80@TYAPR01MB2990.jpnprd01.prod.outlook.com

Branch
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REL_13_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/60369db86f6cc9432626df5a5ccdd9eb3338798e

Modified Files
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src/backend/storage/ipc/shm_toc.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)